1. Field of the Invention
This invention relates generally to a machine for forming a serpentine heat exchanger having a preselected length from a continuous supply of tubing. The machine includes a feed mechanism that advances tubing in preselected increments to a forming and bending head which deforms the section of tubing to be bent prior to successively bending each of the increments in alternative directions.
The tubing is deformed in the bend area into an elliptical or oval configuration having its major axis parallel to the longitudinal axis of the tube and perpendicular to the central axis. During the bending operation the wall in the area of the outer curve moves radially inwardly to decrease the dimension of the major axis due to its inability to elongate sufficiently, while the dimension of the minor axis increases so that a tube passageway having a predetermined design area is maintained. After a predetermined number of successive bending operations have been completed the serpentine heat exchanger formed by the present invention is severed or cut off from the continuous tube at a precise design point to eliminate any need for successive cutting operations and in effect the elimination of scrap and waste is realized.
2. Description of the Prior Art
In the manufacture of serpentine heat exchangers it has been common practice to provide a length of tubing which was bent either between a wheel or shoe with the inside of the tube occupied by a mandrel to maintain the roundness of the tube passageway during the bending operation.
In actual practice it is extremely difficult to provide the exact length of tubing for a particular serpentine heat exchanger to be formed, and, in fact, the length of tubing provided is usually longer than the design length of the completed heat exchanger. This practice is necessary to allow for variations due to stretch and size of bend radiuses. Accordingly the heat exchanger as formed must then be trimmed to the exact length needed for a particular application which, results in a certain amount of waste or scrap.
The practice of employing internal mandrels has many disadvantages, for example, the length of the tubing in the heat exchanger is limited by the length of the mandrel. In practice when using tubes having a 0.375 inch diameter, the maximum practical length of the mandrel has been found to be about 25 feet. As a result, in many instances, several heat exchangers so formed must be joined to provide some of the volume requirement when they are used in refrigeration systems. Other disadvantages arise when the madrel scores the inner wall surface of the tubing which may lead to undesirable refrigerant flow characteristics. The use of internal mandrels also in some instances allow contaminants to be present in the final heat exchanger. These contaminants, when present and if not removed, may lead to blockage in the refrigerant system, especially in restricted areas such as capillary tubes and could result in compressor failure.